The invention relates to a process for coating the surface of pigment or filler particles with an oleaginous and cosmetically functional material.
The coating of pigments for general use in cosmetics is well known in the art. On the one hand, materials are deposited on the pigment surface from aqueous or nonaqueous solutions of said materials via conversion of the materials to insoluble salts as disclosed, for example in U.S. Pat. No. 4,648,908 and dispersing the pigments in solutions of the materials to be deposited, followed by filtering off of the pigments so coated with a film of said materials being adhered to the pigment particle surface.
The coating of oleaginous and cosmetically functional materials onto the surface of pigment particles is also known. Thus, a simple mixing of the components as well as a suspending of the pigments in a solution of the materials to be deposited, followed by separating the solvent, have been done. This is described, for example, in U.S. Pat. No.4,390,524 and DD 209391.
Other known methods relate to depositions via precipitation or adhesion of water-soluble or water-suspendable materials, respectively, onto the surface of pigment particles. U.S. Pat. No.4,622,074 describes a method for uniformly coating the surface of pigments or extender pigments with hydrogenated lecithin via adsorption of a water-insoluble salt. It is further indicated in this patent that it is not possible to coat a pigment with lecithin itself because lecithin is an oily substrate.
The disadvantages of the known processes are as follows: incomplete deposition and dispersion of the oleaginous material onto the particle surface of pigments by simple mixing of the components, and complicated derivatization of natural oily substrates needed to circumvent the coating problem as indicated above for lecithin.
Whenever oleaginous and water-insoluble materials have to be deposited a fundamental disadvantage is the necessary use of organic solvents. Even though deposition of oleaginous materials from solvents results in pigments having advantageous properties, safety and environmental concerns require the use of costly explosion proof manufacturing equipment with the capability of recycling the solvent.